1. Field of the Invention
This invention relates generally to the selective application of chemicals to plants. The invention relates specifically to the use of porous materials for controlling the feeding, distribution and application of liquid agricultural chemicals.
2. Description of Related Art
Conventional methods of applying chemical substances to vegetation include spraying, sprinkling or sowing solutions or mixtures of chemicals over the whole planted area. When such "broadcast" methods are used to kill targeted plants that are near desirable vegetation, unnecessary dilution is required, uneven distribution frequently occurs, chemicals are wasted, the cost of chemicals is increased, adjacent vegetation is subjected to harmful amounts of undesired chemicals, and vegetation far removed from the treatment area is subjected to the chemicals due to "drift", "vaporization", "translocation", or "leaching". Even when selective or beneficial chemicals are distributed by such methods, many of these disadvantages are experienced.
To avoid difficulties associated with the broadcast methods, the individual application of chemicals has been made by hand to selected plants. Selective application has permitted the use of highly potent but relatively safe non-selective herbicides for the control of weeds and other undesirable vegetation. A preferred kind of nonselective herbicide is a 41% solution of isopropylamine salt of N-(phosphonomethyl) aglicine, as further described in U.S. Pat. Nos. 3,799,758 and 4,405,531, and sold under the trademark "ROUNDUP" by the Monsanto Company, Agricultural Products Div., St. Louis, Missouri, 63167.
As disclosed in Laughlin U.S. Pat. No. 2,988,841, mechanical devices have been proposed for the direct application of chemical substances to selected plants. An applicator such as a brush or pad is traversed across the area of vegetation at a pre-selected height, speed and angle, so as to produce a treatment zone without affecting underlying vegetation. Such a mechanical device includes height controlling wheels and a push handle or tractive support, or applicator brushes or pads are adjustably mounted on a rake-like structure.
Mechanical devices for the direct application of chemical substances to plants have been manufactured and sold as attachments to tractors. Hardy et al. U.S. Pat. No. 4,187,638 discloses a rope wick applicator in the form of an elongated pipe having a number of exposed portions of wick protruding from the pipe at spaced locations. Similarly an applicator has been manufactured and sold by Ex-Cell-0 Corporation, Century Engineering Division, Cedar Rapids, Iowa 52401, in the form of an elongated pipe having its lower outer surface covered with a carpet fed with chemical solution.
Weed control at golf courses has been an especially difficult task. As described by Steve M. Batten in his article "Those Irrespressible, Incredible, Impossible Grassy Weeds" in USGA Green Section Record, September/October 1984 pp. 1-4, millions of dollars are spent annually and thousands of hours are devoted to golf course weed control. Weed control methods include scalping, deep-set vertical mowing, turning off irrigation, hand removal, excavation, and starvation by eliminating normal fertilization. Spot application of non-selective herbicide is typically made with hand-held sprayers, plastic squeeze bottles, hypodermic syringes, and paint brushes. Spot application requires the judgment of a person to determine what is a weed or where to place the herbicide. For this reason, this type of weed control has been difficult to automate or conduct with large tractors or maintenance vehicles. However, there are methods to selectively place herbicides such as "ROUNDUP" with large implements. Rope wick applicators can paint the top half of tall fescue or smutgrass above the grown height of desired turfgrasses. Weed kill results by translocation of the "ROUNDUP".
Rope wick or pad applicators have not been sufficiently accurate to selectively kill undesirable vegetation that extends only slightly above the desired vegetation, without causing some damage to the desired vegetation. This basic problem has been found to be related to a number of subsidiary problems including unstable operation of the applicator, undue complexity, inability to cover large areas in a reasonable time period, and the influence of uneven ground, clumps of weeds and foreign objects. In order avoid these difficulties, several improved devices and methods have been invented and set forth in Moore co-pending patent application Ser. No. 820,987, on "Devices and Methods For Selective Application Of Herbicides," filed Jan. 21, 1986.
With regard to the spot application of herbicides to specific plants, another known method is to use a rubber glove having an outer absorbent mitten or sponge which is dipped in a container of herbicide solution and then wiped against undesired vegetation.
Still another method of manually applying herbicide to selected plants is to use an applicator of the kind having a handle carrying a sponge at the lower end of the handle. In one such applicator, advertised under the trademark "Walk A Wick", an applicator bottle containing a supply of herbicide solution is mounted on the upper end of the handle and is provided with a calibration valve for metering a regulated flow of herbicide from the applicator bottle to the sponge. A particular version designated as "Model 200 Pro Applicator" has a cylindrical sponge which may be provided with an optional shield.
While these methods and devices are suitable for applying herbicide to a rather large area of plants by sweeping the applicator or sponge across the undesired vegetation, or to isolated plants by blotting them with a tip of the applicator or sponge, considerable care must be taken to avoid contact with desirable grasses, plants or shrubs as injury may occur. Therefore, these devices are not especially suited for applying herbicide to weeds that are surrounded by and in close proximity to desired plants. Also, the exposed foliage of many kinds of plants is not sufficiently stiff to receive a desired amount of herbicide merely by contact or wiping against an applicator or sponge. In order to avoid these difficulties, several improved manual devices and methods for selective application of chemical substances to plants have been invented and are described in Moore, U.S. Pat. No. 4,716,677, issued Jan. 5, 1988.
Many of the applicators and methods previously available for applying chemicals to plants suffer from one or more of the following deficiencies: inaccurate control of the flow of chemical to the applicator; uneven distribution of the chemical to the applicator surfaces, resulting in a tendency to drip or to have an inadequate supply of chemical available; inaccurate control of flow to various portions of the applicator, particularly when operating on sloping terrain; or poor abrasion resistance of the applicator surface. Other disadvantages include complexity, difficulty of manufacture, poor quality control and high cost.
In an attempt to solve some of these problems, one pad applicator uses an especially configured synthetic sponge which is formed with a relatively dense peripheral skin so that the liquid herbicide received will evenly saturate the entire sponge to prevent uncontrollable liquid flow in localized parts of the sponge. Such a device has several possible disadvantages, including high cost, difficulty of manufacture, lack of abrasion resistance, vulnerability to damage, and being subject to excessive discharge of liquid when pressed or rapidly moved. Since a relatively large supply of liquid at its highest pressure is present within the applicator sponge near its skin, even a small puncture or tear of the skin could cause an undesirable release of this liquid.
There is still a widespread problem of encroachment of turf grasses and weeds into and onto areas that should be kept free of such growth such as flower beds and other plantings, golf course sand traps, paved surfaces, and unpaved barren areas. Costly, time-consuming or damaging methods of controlling such encroachment include spraying of herbicides, mechanical edging, and removal by hand.
Rigid or semi-rigid porous metals, ceramics and plastics have been produced for many years. Porous plastics are manufactured and marketed by Porex Technologies Corp., 500 Bohannon Road, Fairburn, Georgia 30213. Standard Porex products are available in a variety of shapes and sizes, materials of construction, porosities, densities, and resistances to abrasion. Porex publications list "Applicators", "Controlled metering Devices", and "Wicking" devices as products using its porous plastic components. Such products include pens and other inking devices, filters, air diffuser plates, etc. In contrast to sponges and open-cell plastic foam, porous plastic is dimensionally-stable and can be cut, sawed, drilled, tapped and threaded using ordinary wood or metal working tools.